A major challenge in engine oil formulation is simultaneously achieving engine wear protection while also maintaining fuel economy performance, over a broad temperature range. Lubricant-related performance characteristics fuel economy and wear protection are extremely advantageous attributes as measured by a variety of bench and engine tests.
Fuel efficiency requirements for passenger vehicles are becoming increasingly more stringent. New legislation in the United States and European Union within the past few years has set fuel economy and carbon emissions targets not readily achievable with today's vehicle and lubricant technology. In order to improve lubricant fuel economy performance, reduction of lubricant viscosity is one possible path.
Lubricant-related wear control is also highly desirable due to increasing use of low viscosity engine oils for improved fuel efficiency. Due to more stringent governmental regulations for vehicle fuel consumption and carbon emissions, use of low viscosity engine oils to meet these regulatory standards is becoming more prevalent. At the same time, lubricants need to provide a substantial level of durability and wear protection to engine parts due to the formation of thinner lubricant films during engine operation.
High temperature high-shear (HTHS) viscosity is the measure of a lubricant's viscosity under severe engine conditions. Under high temperatures and high stress conditions viscosity index improver degradation can occur. As this happens, the viscosity of the oil decreases which may lead to increased engine wear. HTHS is measured using ASTM D4683, which is incorporated herein by reference. Present day lubricant oils with a high temperature high-shear (HTHS) viscosity of less than 2.9 cP at 150° C. would not be expected to be able to provide acceptable passenger vehicle diesel engine wear and durability performance.
Despite the advances in lubricant oil formulation technology, there remains a need for an engine oil lubricant that effectively improves fuel economy while also providing superior engine antiwear performance.